As an example of a deep ultraviolet LED with a light emission wavelength of 220 to 350 nm, there is known an AlGaN-based deep ultraviolet LED with a design wavelength of 280 nm that has a structure in which a p-GaN contact layer with high absorptance of deep ultraviolet rays is combined with an Au electrode with low reflectivity of deep ultraviolet rays. There is also known a technique of replacing such a p-GaN contact layer with a p-AlGaN contact layer that is transparent to the deep ultraviolet rays, and further replacing the Au electrode with an Al reflecting electrode with high reflectivity, thereby improving the LEE (Light Extraction Efficiency) as well as improving the EQE (External Quantum Efficiency).
Non Patent Literature 1 and Non Patent Literature 2 report that, regarding the above technique, inserting a Ni layer, which is as thin as 1 nm and thus has suppressed absorption of deep ultraviolet rays, between the Al reflecting electrode and the transparent p-AlGaN contact layer to obtain ohmic contact therebetween was found to improve the LEE to 15% and also improve the EQE from 3.8% to 7%.